Taxi drivers' knowledge helps their brains grow

Satellite navigation systems can stunt your brain, preventing it from developing, according to scientists. They have discovered that taxi drivers have actually grown more brain cells because of all the knowledge they keep in their heads.

When the scientists compared the brains of taxi drivers with those of other drivers, they found the cabbies had more grey matter in the area of the brain associated with memory.

They believe that this part of the brain, the mid-posterior hippocampus, is where black-cab drivers store a mental map of London, including up to 25,000 street names and the location of all the major tourist attractions.

The research is the first to show that the brains of adults can grow in response to specialist use. It has been known that areas of children's brains can grow when they learn music or a language.

The scientists warn that increasingly widespread use of satellite navigation - expected to be one of the biggest-selling gifts this Christmas - could change all that.

"GPS [Global Positioning System] may have a big effect," says Dr Eleanor Maguire, who led the research at University College London.

"We very much hope they don't start using it. We believe this area of the brain increased in grey matter volume because of the huge amount or data they have to memorise.If they all start using GPS, that knowledge base will be less and possibly effect the brain changes we are seeing."

In the study, researchers at the Wellcome Trust Centre for Neuroimaging at UCL's Institute of Neurology carried out scans on the brains of 35 cabbies and bus drivers, all men. Various psychological tests were also carried out.

Using bus drivers meant that any brain differences found could not be explained by driving stress, or dealing with passengers and traffic in London. The one big difference between the two is that bus drivers stick to routes, while cabbies have to learn the layout of streets and the locations of thousands of places of interest to get an operating licence.

The results of the scans show that the mid-posterior hippocampus of all the cabbies was bigger and that they had more grey matter than the bus drivers.

Dr Maguire said: "We are now looking at the brains of taxi-drivers before they start training, and at those of retired cabbies to see whether that area of the brain gets smaller when it is not used."